1. Field of the Invention
The present invention relates to storage area networks (SANs) and more specifically to the isolation of inter-integrated circuit buses (I2C buses) in a multiple power domain environment.
2. Description of Related Art
In a SAN environment, storage devices such as digital linear tapes (DLTs) and redundant array of independent disks (RAID arrays) are connected to many kinds of servers via a high-speed interconnection such as Fibre Channel. Standard for Fibre Channel was developed by the American National Standards Institute (ANSI) in the early 1990s specifically as a means to transfer large amounts of data very fast. The Fibre Channel standard can be used for copper cabling or fiber-optic cable at distances of up to 10 kilometers.
In a typical situation, SANs based on the Fibre Channel standard may be initially implemented as a group of server systems and storage devices connected by Fibre Channel adapters to a network. As the SAN grows, hubs and switches can be incorporated. The Fibre Channel standard supports several configurations including point-to-point and switched topologies. In a SAN environment, the Fibre Channel Arbitrated Loop (FC-AL) is used most often to create this high-speed storage network due to its inherent ability to deliver any-to-any connectivity among storage devices and servers. A FC-AL configuration consists of several components including servers, storage devices, and a Fibre Channel switch or hub.
The FC-AL provides not only a high-speed interconnection among storage devices but also strong reliability. In fact, several devices can be removed from the loop without any interruption to the data flow. Also, packets sent over a FC-AL are error-checked and packets can be re-transmitted if any are lost or corrupted. More information regarding SANs and Fibre Channel is provided in an article entitled “Storage Area Networks” from NetworkMagazine.com, the entirety of which is incorporated herein.
RAID arrays and JBODs are housed in disk enclosures. Disk enclosures are devices used to house disk drives. Devices within disk enclosures (e.g., repeaters, enclosure controllers, backplane controllers, memory devices, temperature sensors, port bypass circuits, disk drives, power supplies, and fans) can share an I2C bus to communicate with each other. A problem that may occur is that one of the devices may lose power, thus causing the electrostatic discharge (ESD) diode on its I2C pin to become forward biased to ground. This grounds the I2C bus. When the shared I2C bus is grounded, the other devices cannot communicate with each other even though they remain operational. Thus, what is needed is a disk enclosure that allows other devices to communicate with each other via the I2C bus when one device loses power.